Frequency of ESR measurements

Most of the ESR meters that I have seen test in the 50-200 kHz range. This pretty much covers the switching frequencies of most power supplies, at least in consumer equipment that I am familiar with.

Leonard

Exactly ditto.My Bob Parker meter works at around 100kHz, and I have never had a problem with it picking up any (several per week) faulty caps.

Arfa

"Arfa Daily" wrote in news:1cA6l.115497$ snipped-for-privacy@newsfe01.ams:

one thing to consider is the waveform of the usual switcher;the cap has to deal with a fast rise waveform rich in harmonics.2nd and 3rd harmonics will still have a lot of energy.

your usual 60hz XFMR supplies dealt with a sinewave.

This

Thanks everyone for your replies, you have answered my questions.

On Wed, 31 Dec 2008 01:48:42 -0000, "Arfa Daily" put finger to keyboard and composed:

The following diagram and flowchart indicate that, at least for the Mark 2 design, the capacitor under test is pulsed with 8us constant current pulses repeated every 500us:

- Franc Zabkar

That does appear to be so. Without looking it up, I just had it fixed in my head that it was around 100kHz. With the fact that it is a highly asymmetric waveform, duty factor-wise, I guess that it's hard to quote it as an actual frequency. It's sort of 100+ kHz 'width' pulses, repeated at a frequency of

Arfa

So, its a 2 Khz signal with 2000/100000 = 2 % duty cycle =

On Thu, 1 Jan 2009 01:14:42 -0000, "Arfa Daily" put finger to keyboard and composed:

Remember that they're also current pulses, not voltage pulses, so the voltage appearing across the cap is a trapezoid. I don't know how this compares with a meter that generates a sinusoidal test voltage, assuming that's how others do it.

- Franc Zabkar

The Capacitor Wizard uses a 100Khz sinusoidal signal. The Bob Parker design is as described - that is what is used in our Blue ESR meter. Bob always represented that his method is the equivalent of a 100Khz signal.

Other designs are described in our comparison at

John AnaTek Corporation

Ah. So that's where I got it from. Direct from Bob .... Arfa

I have this meter:

:>

:>

:> >I have a question about ESR measurements. :>

:> > I have been doing some reading about ESR and the literature indicates :> > it can be a strong function of frequency.  In the design a SMPS  I :> > assume the ESR of importance is at  switching frequencies (at least :> > for the line side capacitor). :>

:> > I have also noticed that often the measurement made in trouble :> > shooting are low frequency measurements (step function - looking at :> > the abrupt change in voltage). :>

:> > Is the above accurate and if so when a cap goes bad do the low :> > frequency measurements catch the majority of the high frequency ESR :> > failures.  Are there significant failure modes where a low frequency :> > ESR measurement would miss the higher frequency ESR failure? :>

:> > Thanks Much, :>

:> Most of the ESR meters that I have seen test in the 50-200 kHz range.  This :> pretty much covers the switching frequencies of most power supplies, at :> least in consumer equipment that I am familiar with. :>

:> Leonard : :Thanks everyone for your replies, you have answered my questions.

Now to throw in a curve ball...

In designing his Tan-Delta meter, Cyril Bateman used 100Hz sine. His theory was that using 100KHz could cause the measuring lead inductance to exceed the self inductance of the capacitor under test and thus complicate the accuracy of the result.

Just out of curiosity, has anyone tried using an infrared thermometer to try and find bad or failing caps. I did a quick search on the on the internet and found units you can get for as little as $20. The spot size is very small and I believe the top of the cap is an ideal target. Could use a black sharpie to make a small black spot for even better measurements. A SMPS cap which had a High ESR should read high in temp, might be more sensitive than using your finger to test for temperature. An open or failed cap should read low. Of course the unit being tested couldn't be completely dead. If it worked one nice feature would be being able to identify bad caps before even removing the PC board.

The power dissipated in the cap should be proportional to the increase in ESR ,the temperature increase should be on the fist order equal to the power dissipated in the cap. So if the original temperature rise due to the new caps ERS was 1 degree C and the ESR increased by a factor of 10 the old caps temperature should be about

Might be able to find bad IC's as well. Perhaps the increase in sensitivity using this device would help find other failing or failed components as well. Might also be useful in identifing failing or failed components in very high voltage circuits. Those components you would not want to touch with power on.

Don't know if the idea has any merit but thought I would mention it.

Gordon ,

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Back to ESR measurements,

In the past I have had any test equipment available to me I wanted. At this point I am trying to collect test equipment on a very limited budget. So my interest in ESR testers.

Thanks again everyone for all the info. I have summarized below what I think I am hearing here and other places. I would appreciate any comments to the validity of the statements below.

Inexpensive =93bog - standard=94, In Circuit ESR measurements of Caps in trouble shooting =93consumer electronics=94 came about due to the Common and Sever Failure Mode of Dried Out Electrolytic Capacitors. The ESR changed by a factor of 10X to 30X so was easy to pick up with simple inexpensive in circuit ESR testers. These meters are a great tool to have in a persons toolbox to expedite greatly trouble shooting of failed or troubled circuits due to this capacitor failure mode.

If used for this purpose, due of the severity of the failure mode (10X to 30X increase in ESR), you don't necessarily need to be too concerned with accuracy. Many different meters designs out there which may give different readings between themselves, each do a great job helping to finding a large majority of capacitors that are causing circuit problems due to this failure mode.

In trouble shooting consumer electronics for this failure mode, what is more important is that you get a feel for what your particular meter readings mean for electrolytic capacitors with different parameters such as Capacitance, Temperature Rating and the importance of low ESR in the particular type of circuit you are trouble shooting (for example some caps may measure higher ESR's because they were not low ESR Caps to begin with).

I can imagine that good calibration between the SAME design of meters might come into play if people want to compare results to assess each others expertise in trouble shooting this failure mode for different electrolytics and circuits . Even here the requirements may be fairly low since the failures are so sever (10X to 30X)

This is an exaggeration but an INEXPENSIVE IN CIRCUIT ESR tester could be compared to a 12 volt sensor in trouble shooting a cars electrical system. It does not need to be a very accurate tool and may not be the right tool to use in all situations but it is A VERY USEFULL TOOL. Many different simple designs of the voltage sensor work well.

For other lower failure rate capacitor problems other In or Out of circuit testers such as capacitance meters, capacitance leakage meters, testers that can test capacitor parameters nearer their operating conditions such as voltage of operation, imposed voltage (or current) waveform and magnitude and frequency, are useful tools.

For these lower failure rate capacitor failures, another low overhead and perhaps time saving approach is to pin point the circuit that is having problems and replace a suspected capacitor with a known good capacitor to determine if the capacitor is part of the problem.

Thanks again for all of your responses, information and sharing your experience,

Jeroni Paul, I really like the LM324 ESR meter

On Fri, 2 Jan 2009 11:11:21 -0000, "Arfa Daily" wrote:

: :"Ross Herbert" wrote in message :news: snipped-for-privacy@4ax.com... :> On Wed, 31 Dec 2008 09:30:11 -0800 (PST), snipped-for-privacy@gmail.com wrote: :>

:> :On Dec 30, 6:27 pm, "Leonard Caillouet" wrote: :> :> wrote in message :> :>

:> :> :> news: snipped-for-privacy@w1g2000prm.googlegroups.com... :> :>

:> :>

:> :>

:> :> >I have a question about ESR measurements. :> :>

:> :> > I have been doing some reading about ESR and the literature indicates :> :> > it can be a strong function of frequency. In the design a SMPS I :> :> > assume the ESR of importance is at switching frequencies (at least :> :> > for the line side capacitor). :> :>

:> :> > I have also noticed that often the measurement made in trouble :> :> > shooting are low frequency measurements (step function - looking at :> :> > the abrupt change in voltage). :> :>

:> :> > Is the above accurate and if so when a cap goes bad do the low :> :> > frequency measurements catch the majority of the high frequency ESR :> :> > failures. Are there significant failure modes where a low frequency :> :> > ESR measurement would miss the higher frequency ESR failure? :> :>

:> :> > Thanks Much, :> :>

:> :> Most of the ESR meters that I have seen test in the 50-200 kHz range. :> This :> :> pretty much covers the switching frequencies of most power supplies, at :> :> least in consumer equipment that I am familiar with. :> :>

:> :> Leonard :> : :> :Thanks everyone for your replies, you have answered my questions. :>

:>

:> Now to throw in a curve ball... :>

:> In designing his Tan-Delta meter, Cyril Bateman used 100Hz sine. His :> theory was :> that using 100KHz could cause the measuring lead inductance to exceed the :> self :> inductance of the capacitor under test and thus complicate the accuracy of :> the :> result. : :The thing is with a bog-standard ESR meter, it's all about relative :measurements, 'feel', experience, and intuition rather than accuracy. :Determining whether or not an electrolytic is faulty by way of its ESR, is a :bit of a black art, and is with any ordinary 'in-circuit' ESR meter. The :reading just gives you some help and 'feel good' backup. This is why I have :contended on many occasions that such an instrument is not one of absolutes, :and cannot be just picked up and used to give 'go / no go' definitive :answers about the state of a cap, by anyone who chooses to buy one. It's :just a helper that gives you one more pointer, allbeit a mostly pretty good :one, without having to remove the cap (generally) from the circuitry that :it's in. : :The thing is with the inductance argument, I would have thought that given :that the self inductance of a 'standard' electrolytic is quite high due to :the way they are constructed, the inductance of the test leads would have :been pretty insignificant in comparison ?? : :Certainly, in practice, if it is a 'problem', it has never caused me any :trouble with using my Bob Parker to help identify bad 'uns ... : :Arfa :

I agree entirely. With regard to everyday servicing you only really require a "relative" indication. In some cases some intuitive interpretation on the part of the user is required to determine whether a cap is "bad" and requires replacing. Obviously, if the indication is way too high it doesn't take any intuition to decide to replace.

A very good example of this occured on my bench last Friday. I had a Sony DVD / HC that was very 'iffy' at the beginning of a disc. It would freeze and pixellate pretty much at random, but if you left it and it managed to get past the intro without totally falling over, it would play ok for the rest of the disc. On auto setup, it would proceed ok on single layer and CD discs, but fail every time on a dual layer. I had a laser for the model on the shelf, so tried it, but it was just as bad. I then turned my attention to the little servo board under the deck, where there were several surface mount electrolytics. For no other reason than that similar caps in a similar location give all sorts of odd problems on many of the Sony CD players from a few years ago, I got out the ESR meter, and ran it over these caps. Now I don't know about your experience of ESR and SM electros, but I've always found that even with brand new ones, the ESR is significantly higher than you would expect for the same value and voltage of a through-hole type.

There were two 22uF 10v ones on the board, and the first one measured 5 ohms. Now if that was a through-hole one, you'd immediately say it was bad, but for a SM, that is quite possibly a satisfactory figure. When I measured the other one, it went 3 ohms, so I found another similar one on another board, and measured that. It also went about 3 ohms. So, based on the fact that two of them read one value, and a third read a slightly different amount, I applied experience, gut feeling and the measurements, and went ahead and replaced it. Result ? Total cure, and the ESR meter played only a supporting role in achieving that.

Arfa

John-

I built one of your Blue ESR meter kits and am impressed with it.

Somewhere I read that there is an industry specification or common practice, that requires ESR measurement to be made at 100 KHz. If it is in fact a "standard" method, you should petition that standards committee to agree that your method is equivalent.

As others commented, approximate methods for measuring ESR may be adequate for detecting common failures. However, I do not think the Bob Parker method is approximate. As long as there is no significant inductance involved, it seems to be quite accurate. Try putting resistors in series with low-ESR capacitors. Taking the low ESR into account, the meter should measure close to the same value as when connected across the resistors alone. I expect it will agree with other methods of measuring the resistors. Certainly better than ten percent!

Fred

: Just out of curiosity, has anyone tried using an infrared :thermometer to try and find bad or failing caps. I did a quick search :on the on the internet and found units you can get for as little as :$20. The spot size is very small and I believe the top of the cap is :an ideal target. Could use a black sharpie to make a small black spot :for even better measurements. A SMPS cap which had a High ESR should :read high in temp, might be more sensitive than using your finger to :test for temperature. An open or failed cap should read low. Of :course the unit being tested couldn't be completely dead. If it :worked one nice feature would be being able to identify bad caps :before even removing the PC board.

Since electronic equipment (particularly SMPS) will generally run fairly warm under normal loading the whole unit will become warm throughout after some time. In order to determine a bad cap using thermal means would require the background component temperatures to be used as a base reference and discounted from the temperature of the cap being tested. It would be somewhat equivalent to sticking a finger on each cap to see if it was warmer than the average temperature of other components - but I wouldn't recommend this in working equipment.

In some circuits (SMPS) a bad cap will prevent the unit from operating at all and then you have no way of measuring by thermal means.

Not a valid faulty cap finding method IMO.

: : The power dissipated in the cap should be proportional to the :increase in ESR ,the temperature increase should be on the fist order :equal to the power dissipated in the cap. So if the original :temperature rise due to the new caps ERS was 1 degree C and the ESR :increased by a factor of 10 the old caps temperature should be about :10 deg higher, easy to measure. : : Might be able to find bad IC's as well. Perhaps the increase in :sensitivity using this device would help find other failing or failed :components as well. Might also be useful in identifing failing or :failed components in very high voltage circuits. Those components you :would not want to touch with power on. : : Don't know if the idea has any merit but thought I would mention it. : :Gordon ,

I have not heard of any such industry specification but will investigate and report back to this group.

Does anyone else have any insight into this?

John AnaTek Corporation The Blue ESR kit at